1. Field of Invention
The present invention relates generally to the field of wireless communication networks. More particularly, in one exemplary aspect, the present invention is directed to methods and apparatus for operation of a Single Frequency Network (SFN) using signal “shaping” to enable resolving individual signal components, such as for services including location determination.
2. Description of Related Technology
The Worldwide Interoperability for Microwave Access (WiMAX) technology is based on the IEEE 802.16 Standard, which is also commonly referred to as Wireless Metropolitan Area Network (WirelessMAN). WiMAX is within consideration for support of future evolution to fourth generation (4G) technology.
Current implementations of WiMAX (i.e., IEEE Std. 802.16e) are based on Scalable Orthogonal Frequency Domain Multiple Access (S-OFDMA), which can flexibly trade frequency and time resources for varying data requirements (such as high transmission robustness, high data throughput, low latency, etc.). The flexibility of S-OFDMA allows WiMAX to support long distance, low-bandwidth telecommunications, or short distance, high-bandwidth transmissions. Furthermore, WiMAX can also be adapted for focused point-to-point communication, or geographically diffuse cellular network applications.
Typical cellular communication systems exploit a wireless link between client or mobile devices (e.g., User Equipment (UE) in a 3G network) and Base-Stations (BS) to exchange information. In regard to downlink transmissions (i.e. BS transmitting to client or UE), cellular systems can be classified as either: (i) a one-to-one communication, where a single BS is communicating with a single UE; or (ii) a many-to-one communication, where multiple Base Stations are communicating with a single UE.
Referring to FIG. 1A, in one typical implementation of a prior art WiMAX cellular network 100, multiple S-OFDMA base stations 102 simultaneously transmit identical data streams across the same frequency within respective wireless coverage areas 104. This form of network architecture (not limited to WiMAX networks) is also commonly referred to as a Single Frequency Network (SFN). As shown, BS1 102A, BS2 102B, and BS3 102C—having wireless coverage areas 104A, 104B and 104C, respectively—each provide a unique path to the UE 106. These channel characteristics can be symbolically demonstrated with a Channel Impulse Response (CIR) 108A, 108B, 108C, where an impulse transmitted from each BS in a “vacuum” is represented with its incident response at the UE antenna.
Single Frequency Networks have unique advantages and disadvantages compared to other one-to-one cellular systems. In certain applications, SFNs may provide better coverage than their one-to-one counterparts. Two or more SFN base stations may cooperate such that within their overlapping coverage areas, their signals incident at the receiver constructively interfere. SFN base stations may advantageously use this “beamforming” capability to efficiently utilize spectral resources. Unfortunately, due to the nature of SFN synchronicity, both receiver and base stations implementations have significantly more complexity when compared to their one-to-one counterparts.
FIG. 1B illustrates an aggregate BSN CIR at the UE 106. As shown, the array of BSs 102A, 102B and 102C may be modeled with a superimposition of the previous CIRs 108A, 108B, and 108C from each individual BS creating a single-source transmission from an aggregate BS 102ABC with a corresponding aggregate channel impulse response 108ABC. The UE does not have any method of identifying which portion of the aggregate impulse was generated by which BS. In standard prior art operation, the UE does not need to identify the originating BS for each received data stream. Instead, the UE uses a standard single-source decoder to extract the data, treating each incoming data stream as separate “diversity” streams. This is also commonly referred to as macrodiversity (where the distance between diversity antennas is much greater than the wavelength of operation).
Location Determination Services
A current topic of interest in wireless (e.g., cellular) networks is the determination of physical location. Physical location has a wide variety of applications for both subscribers, as well as for generalized network operation. The desirability of location management services within cellular networks is evidenced by the deployment of Global Positioning Satellite (GPS, as well as Assisted GPS or AGPS) receiver functionality within cellular phones. The first handsets with integrated GPS were available for broad consumer availability on networks in 2002 in response to, inter alia, U.S. FCC mandates for handset positioning in emergency calls. Development of location-based services for widespread customer access by network, and third party software developer features were slower in coming, but have gained in popularity as of the date of this filing.
Some common applications utilizing user location information include navigation aids, child safety/location, and fleet management. A typical consumer street navigation aid receives an input location coordinate and calculates optimal directions to a destination location using internally stored street maps. Other uses for personal navigation devices may include hiking, and/or other outdoors based activities in unfamiliar semi-urban/rural areas. In addition, many businesses use location management devices for fleet management. Fleet management devices are used to track the locations of vehicles to improve productivity, resource management, and/or delivery efficiency.
The network operator may also advantageously implement location determination services within subscriber equipment. As previously mentioned, one example of location determination required by the network operator is the Emergency 911 (E911) physical location service. During an E911 call, a cellular phone is required to report its current physical proximity, to assist in deployment of emergency services.
Current E911 implementations within cellular networks may utilize the aforementioned Assisted GPS (A-GPS) system or complete GPS solutions. For low-cost devices, location determination may also be achieved by triangulating signals originating from distinct Base Stations. Since the User Equipment cannot distinguish overlapping signals the various signals must be orthogonal in time or frequency. Dedicating such time or frequency resources for location determination is costly, and inefficient.
As discussed previously, most current solutions for location determination utilize a GPS, or an assisted GPS (AGPS) receiver. Other solutions for global positioning, such as GLONASS (Russian), Galileo (European Union), Beidou (China), etc. also use similar satellite reception technologies. A GPS receiver comprises a high gain antenna, processing chip, and a very precise timekeeping device. Due to the high attenuation of satellite signals and relatively specialized nature of satellite reception, a GPS unit is typically bundled together, and implemented in isolation from the other cell phone components.
Referring to FIG. 2A, an exemplary GPS system 200 comprising a prior art GPS receiver 206 operating within a system or constellation of satellite transmitters 202 is illustrated. The GPS receiver receives a time varying satellite transmission from each satellite. All GPS satellites are synchronized to a single “GPS time reference”. The GPS receiver then uniquely identifies each received satellite transmission. The time varying nature of each satellite transmission is used with reference to the GPS receiver's own time reference. By collecting sufficient data from multiple satellites, the GPS receiver can ascertain the absolute “GPS time reference”, and corresponding propagation time for each received individual GPS signal. The propagation time for each received GPS signal is used to calculate the distance between each satellite and the GPS receiver. Using the distances from each individual satellite, and the known location of each satellite with respect to the Earth 250 (calculated with the assistance of the ephemeral data embedded within each satellite transmission), the GPS receiver can determine its exact location.
Referring to FIG. 2B a simplified diagram of triangulation of a GPS receiver 206 within a two dimensional plane is shown. The locations of the satellites 202A, 202B, and 202C are known, and expressed in coordinates C1, C2, and C3. The propagation distances d1, d2, and d3 are determined based on the propagation time multiplied by the speed of light (c). As is shown, a distance d1 from a first coordinate C uniquely identifies a ring of points r1. An additional distance d2 from a second coordinate C2 uniquely identifies two points within the plane: p2, and p3. By including, yet another distance d3 from a known coordinate C3, a unique single point in the two-dimensional plane is described: p3. Therefore, given a known coordinate system, and sufficient path information, a GPS receiver can calculate its unique position p3.
In a typical GPS receiver, at least five satellites are required to pinpoint the GPS receiver's location (the additional 3rd spatial dimension requires a fourth additional satellite; yet another fifth additional satellite is required to remove timing ambiguity). Typically, a number greater than five is necessary to improve timing and channel accuracy. Additional satellite information improves coordinate accuracy and time reference.
In addition to the GPS/AGPS solutions discussed above, several solutions have been contemplated for location determination within SFN systems. For example, United States Patent Publication No. 20050148340 to Guyot published Jul. 7, 2005 and entitled “Method and apparatus for reporting location of a mobile terminal” discloses a method for use by a wireless communication network in responding to a request originating from a requester for an estimate of the position of a mobile terminal. The request is provided via an LCS server along with a requested accuracy. The method includes a step in which a controller of the radio access network by which the mobile terminal is coupled to the cellular network provides a response to the request including not only the position/location estimate but also either the accuracy of the estimate in a form directly useable by the LCS server (e.g. in same form as the requested accuracy), or an accuracy fulfillment indicator, i.e. an indication of whether the accuracy of the estimate is at least as good as the requested accuracy.
United States Patent Publication No. 20050186967 to Ozluturk published Aug. 25, 2005 and entitled “Multi-network location services support” discloses apparatus and methods for location of a portable device with a transmitter, such as a wireless transmit/receive unit (WTRU) in a cellular telecommunications network, which is obtained by a primary network augmented by data obtained from a diverse network. In a particular configuration, changes of the indication of the location, of the portable device are used to update positional information, such as positional information obtained from a GPS receiver.
United States Patent Publication No. 20050266855 to Zeng et al. published Dec. 1, 2005, entitled “Method and system for radio map filtering via adaptive clustering” discloses a method for estimating a location of a wireless device in a wireless local network. The method includes forming a first set comprised of the signal strength received from access points that the wireless device received a signal from and an indicator of no signal strength measured for access points that the wireless device did not receive a signal from. Next, a scan subset can be formed comprised of access points in the first set that has associated signal strength. Next, a cluster comprised of the calibration points can be formed based on the scan subset. A distance between the first set and each of the calibration point in the cluster can be calculated. Then, the smallest distance can be selected as the location estimate.
Chinese Patent Publication No. CN1791266 to Duan, published Jun. 21, 2006 and entitled “Urgent calling method capable of rapid positioning” discloses a fast-location emergence call method comprising; the mobile platform sending the emergency call request information with location detection information to wireless network controller to transfer to mobile exchange center; the latter builds the emergency call between mobile platform and emergency help center according to information and locates the mobile platform. Wherein, the said information is the detection result of SFN-SFN observation time difference of two base station sub area signal after wireless network controller sending detection control information.
United States Patent Publication No. 20060240843 to Spain et al., published Oct. 26, 2006 and entitled “Estimating the location of a wireless terminal based on non-uniform locations” discloses a technique for estimating the location of a wireless terminal at an unknown location in a geographic region. The technique is based on the recognition that there are traits of electromagnetic signals that are dependent on topography, the receiver, the location of the transmitter, and other factors. For example, if a particular radio station is known to be received strongly at a first location and weakly at a second location, and a given wireless terminal at an unknown location is receiving the radio station weakly, it is more likely that the wireless terminal is at the second location than at the first location.
U.S. Pat. No. 6,011,974 to Cedervall, et al. issued Jan. 4, 2000 entitled “Method and system for determining position of a cellular mobile terminal” discloses a method and system by which a round-trip calculation is used to determine the distance between a mobile radio station (MS) and a radio base station (BS) using the apparent uplink and downlink signal propagation air-times (e.g., T-up and T-down). As such, no absolute time reference is required. The MS and BS report to a service node in the mobile network the local departure and arrival times of the uplink and downlink signals, and calculate the apparent air-times, T-up and T-down. The distance, D, between the MS and BS can be calculated as D=c(T-up+T-down)/2, where “c” equals the speed of light. The distances, D1, D2 and D3, to at least three base stations whose locations are known, can be used in a triangulation algorithm to determine the MS's position.
WIPO Publication No. 2007/112696 published Apr. 4, 2007 to Zhang and entitled “Method and system for realizing multimedia broadcast multicast service” discloses a method and a system for realizing multimedia broadcast multicast service. While receiving the multimedia broadcast multicast service in a SFN network, the user equipment obtains the idle transmission interval time slot in a transmission interval between two successive frames or in a transmission interval of a frame via the compression mode or data scheduling by the schedule unit. The user equipment could handover to the LTE network (or other networks) to perform measurement, registration or paging correspondence as required. The user equipment could handoff to the LTE network to perform cell reselection or location area update during the transmission interval time slot based on the measurement results. When receiving a call, the user equipment could handoff to the LTE network to send a rejection-receiving-message or receive corresponding service during the transmission interval time slot.
United States Patent Publication No. 20070202880 to Seo et al. published Aug. 30, 2007 and entitled “Method of estimating location of terminal in switched-beamforming based wireless communication system” discloses a terminal location estimation method in a wireless communication system in which an access point (AP) provides an access service to a plurality of terminals that includes defining a plurality of beam spaces around the AP through space multiplexing; scheduling the beam spaces according to a predetermined pattern; simultaneously forming a beam in at least one beam space; and detecting the existence and location of a terminal according to whether a response message in response to the formed beam is received. Accordingly, an AP forms beams in a predetermined scheduling pattern, and each of the terminals detecting the beams registers its location by informing the AP that each of the terminals exists in a relevant beam area, and thus, a location of each of the terminals can be estimated without using a complex DOA algorithm.
United States Patent Publication No. 20070225912 to Grush published Sep. 27, 2007 and entitled “Private, auditable vehicle positioning system and on-board unit for same” discloses a system and method to generate a private, auditable, evidentiary quality record of the location-history of an asset or person. Grush addresses ten improvements over existing systems that are proposed or used for metering for payment services for tolling roads, parking or pay-as-you-drive insurance, namely, cost-effective location accuracy in harsh signal environments, evidentiary assurance of location estimation, handling of dynamic and stationary positioning in a single device, high-ratio compression for a set of stationary positions in urban canyon, high-ratio compression for a dynamic tracklog in urban canyon, high-ratio compression for a set of asset motion behaviors, a method of remote device health check, including anti-tampering, removal of residual price assignment errors, anonymous use without on-board maps, and a method of deconsolidating payments to multiple payees with multiple payment regimes. This system can be applied to road-pricing, congestion-pricing, metered-by-the-minute parking and pay-as-you-drive insurance, incorporating privacy management, and legal admissibility of the evidentiary record. This same device can also be applied to vehicular fleets, military ordinance, or other location audits for assets whether motorized or not, as might be needed in evidence of contract fulfillment or other forms of non-real time geofencing audits.
United States Patent Publication No. 20080004042 to Dietrich et al. published Jan. 3, 2008 and entitled “Enhanced wireless node location using differential signal strength metric” discloses a wireless node location mechanism that employs a differential signal strength metric to reduce the errors caused by variations in wireless node transmit power, errors in signal strength detection, and/or direction-dependent path loss. As opposed to using the absolute signal strength or power of an RF signal transmitted by a wireless node, implementations of the location mechanism compare the differences between signal strength values detected at various pairs of radio receivers to corresponding differences characterized in a model of the RF environment. One implementation searches for the locations in the model between each pair of radio receivers where their signal strength is different by an observed amount.
Despite the variety of the foregoing approaches, current location determination capabilities for UEs require large amounts of dedicated resources, such as additional integrated circuits, processing overhead, and/or increased power consumption. These requirements come at an appreciable cost, whether in terms of actual monetary cost of manufacturing the UE or providing the user's subscription service, or in terms of reduced performance (e.g., reduced battery life, etc.). Accordingly, there is a salient need for improvements to current solutions for mobile device location determination.
Ideally, such improved methods and apparatus would work in existing wireless or cellular network infrastructure with little to no replacement of current hardware deployments, and minimal to no impact on software configuration. Such methods and apparatus would also be transparent to non-enabled UE.
Furthermore, a desirable solution would provide estimations of UE location to within a certain level of accuracy, so as to facilitate and support services which require such level of accuracy in order to be useful to the subscriber.
In addition, such improved apparatus and methods would obviate the need for expensive and/or dedicated hardware components, such as those commonly used for a satellite co-receiver (e.g. GPS).
These improved apparatus and methods would also advantageously leverage existing network (e.g., single frequency network or SFN) topology to enable a UE to identify its location regardless of where in the network it is actually located; i.e., without “holes” in location determination coverage.